1. Field of Invention
This invention provides a means for measuring the polarity and the intensity of radiation that fall within the spectral ranges of extreme ultraviolet (EUV), soft x-ray (SXR), and x-ray (XR) radiation.
2. Description of Related Art
The measurement of the degree of polarization and the intensity of polarized EUV, SXR, and XR radiation are important in a number of fields of research. For example, these measurements may be used in the analysis of hot dense plasmas in thermonuclear research, in astronomical observation of stars and the sun, in investigations of interactions of ions, atoms, and molecules with solid surfaces, and in the determination of fundamental atomic constants in x-ray diffractometry.
As seen in FIG. 1, a beam of radiation 100, incident upon a smooth, flat, reflective, surface 102 at any arbitrary angle 104, is conveniently represented by two vibrations: one parallel and one perpendicular to the plane of incidence. Standard notation refers to these components as Es (s-perpendicular component) and Ep (p-parallel component). The polarization of radiation is generally measured by comparing the differences between the coefficients of reflection of the Es and Ep components of the radiation beams from optical surfaces. The coefficient of reflection is defined as the ratio of the intensity of radiation reflected from an optical surface divided by the intensity of radiation directed onto that surface. The degree of polarization P is defined as follows:
P=|Esxe2x88x92Ep/Es+Ep|
Prior art methods and devices utilized to measure the degree of polarization of EUV, SXR, and XR beams generally involve measurements of the coefficients of reflection from a reflective surface, such as a crystal or multi-layer x-ray mirror, when the incidence of the beam relative to the reflective surface (xcex8) is at an angle close to the total polarization angle (Brewster""s angle). The total polarization angle for EUV, SXR, and XR radiation is typically between 41 to 49 degrees.
Referring to FIG. 2, prior art devices generally utilize a measurement system 200 comprising a reflective surface 202, e.g., a multi-layer mirror or crystal, a detector or sensor 204, and a filter 206. A beam of radiation 212 from a source 210 passes through filter 206, which removes unwanted radiation from the beam. Once beam 212 passes through filter 206, it falls on reflective surface 202 and is reflected to detector 204, which is adapted to measure the intensity of beam 212. The radiation reflected by reflective surface 202 is monochromatic because reflective surface 202 absorbs all but a narrow band of reflected radiation. Reflective surface 202 is then rotated around an axis 208 that is parallel to beam 212 so that beam 212 can be measured in different planes of vibration. In order to measure beam 212 in different planes, detector 204 may be rotated in unison with reflective surface 202.
Once measurements have been obtained of the intensity of the radiation in different angular positions around axis 208, the measurements can be used to determine the polarity of the radiation. This method is applicable for measuring the polarization of continuous beams of radiation at wavelengths below 35.0 nm.
One of the disadvantages of this method is that reflective surface 202 is only capable of reflecting a narrow band of radiation at an angle of 45 degrees. Radiation with greater or lesser wavelengths outside of this band of radiation is absorbed by the reflective surface. In order to measure wavelengths outside of this narrow band, it is necessary to change the reflective surface. Moreover, in the wide spectral region with wavelengths greater than 30.0-50.0 nm, the polarization of a beam of radiation results in multiple reflections from flat metallic mirrors (i.e., mirrors covered with gold), when the mirrors are rotated around the axis of radiation. To perform polarization measurements, preliminary monochromatization of the beam of radiation is required by means of a diffraction grating. However, incorporating a diffraction grating complicates the construction of the polarization device and decreases its brightness.
The processes and systems of the present invention are based upon:
1. The enhancement of differences in the reflection properties of p and s polarized beams of EUV, SXR or XR radiation following multiple reflections of radiation from optical smooth surfaces (including multi-layer mirrors and crystals);
2. The guiding and focusing of beams of EUV, SXR and XR radiation resulting from multiple reflections of radiation from inner optical smooth surfaces of single capillaries (including capillaries with additional reflectance layers on the inner surface) in polycapillary bundles; and
3. The analysis of the spectral components of beams of EUV, SXR, or XR radiation following their reflection from dispersive optical elements such as multi-layer mirrors or crystals.
The reflectance of EUV radiation from a smooth surface is different from the reflectance of SXR or x-rays. For SXR, the difference between Es and Ep is smaller than 10xe2x88x922, while for EUV the distinction between Rs and Rp is relatively large. For EUV radiation, the Total Reflection Coefficient (R) is seen to be rather large (R≈0.85-0.95, up to the angle of incidence xcex8 greater than 85xc2x0) assuming multiple reflections of EUV radiation inside a capillary, particularly a curved capillary, but which occurs in any capillary array. This has been successfully demonstrated experimentally. The substantial difference between Es and Ep for EUV radiation provides the opportunity for the measurement of the degree of polarization of EUV radiation using capillary array technology.
A most advantageous application of this invention is the ability to measure at the same time the polarization and spectral characteristics of the radiation beam. Because these processes and devices can focus the polarized radiation beam onto the detector, an additional advantage is their ability to aid in the analysis of weak beams of radiation. This invention can be used in the diagnostics of hot plasma, in x-ray astronomy, in atomic physics, surface analysis, crystallography, medical and biological x-ray diffractometry, and x-ray microscopy.
Briefly stated, the present invention comprises a system for measuring the polarization and intensity of extreme ultraviolet, soft x-ray, and x-ray radiation produced by a source of radiation. The system comprises a reflective surface, a capillary array, and a detector. The reflective surface is adapted to reflect the radiation produced by the source. The capillary array is adapted to transmit the radiation. The capillary array comprises a receiving end positioned to receive the radiation reflected by the reflective surface and an emitting end. The detector is positioned to receive radiation emitted by the emitting end of the capillary array, the detector being adapted to measure the intensity of the emitted radiation.
The above description sets forth, rather broadly, the more important features of the present invention so that the detailed description of the preferred embodiment that follows may be better understood and contributions of the present invention to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and will form the subject matter of claims. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangement of the components set forth in the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.